A drill chuck connectable to a drill spindle is known comprising a plurality of clamp jaws forming between themselves a receptacle for a drill tool, a chuck body in which the clamp jaws are arranged symmetrically about the rotation axis and are guided in a direction inclined to the rotation axis, and a tightening ring mounted on the chuck body coaxial to the rotation axis, which is mounted rotatably by axially nonshiftable on the chuck body, and, for moving the clamp jaws, has a tightening thread coaxial with the rotation axis which is engaged with a row of teeth provided on each of the clamp jaws.
A drill chuck of this type, is for example, described in German Patent No. 34 16 986 In this drill chuck the threaded opening for mounting the chuck on the drill spindle is located in the chuck body and clamping of the drill tool is effected with the help of a chuck key insertable in the chuck body. The chuck has a pinion engageable in a toothed ring provided on the tightening ring. With the help of this chuck key the tightening ring can be rotated by the pinion on the key to open or close the drill chuck. An automatic aftertightening or self tightening of the drill tool is not possible in this drill chuck by the action of forces arising in drill operation.
By contrast to this type of chuck, an aftertightening or selftightening drill chuck has a basically different structure. In that drill chuck the clamp jaws are -located in a jaw holder separated from the drill chuck and guided on a conical surface of a tightening cone of the tightening ring so that the clamp jaws are movable radially to the axis of the drill tool receptacle by an axial relative motion between the tightening cone and the jaw holder.
The jaw holder is rotatable with a central threaded bolt on a tightening thread provided on the chuck body for axial relative motion. The jaw holder, the tightening jaws and the tightening ring are connected nonrotatably with each other.
In one such drill chuck described in German Patent No. 28 15 026, a clamping both manually with the tightening ring and also an automatic aftertightening by reaction moment of the drill tool during drill operation is possible, since the torque resistance of the drill tool causes a tightening motion by the clamp jaws in the jaw holder connected nonrotatably with them in the same way as the tightening ring.